Packaging photon building blocks with top side connections and interconnect structure

ABSTRACT

Standardized photon building blocks are used to make both discrete light emitters as well as array products. Each photon building block has one or more LED chips mounted on a substrate. No electrical conductors pass between the top and bottom surfaces of the substrate. The photon building blocks are supported by an interconnect structure that is attached to a heat sink. Landing pads on the top surface of the substrate of each photon building block are attached to contact pads disposed on the underside of a lip of the interconnect structure. In a solder reflow process, the photon building blocks self-align within the interconnect structure. Conductors on the interconnect structure are electrically coupled to the LED dice in the photon building blocks through the contact pads and landing pads. The bottom surface of the interconnect structure is coplanar with the bottom surfaces of the substrates of the photon building blocks.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/987,148, filed Jan. 9, 2011, which is incorporated herein byreference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to packaging for light-emittingdiodes, and more particularly, to a photon building block that can bepackaged alone as an emitter or together with other photon buildingblocks as an array of emitters.

BACKGROUND INFORMATION

A light emitting diode (LED) is a solid state device that convertselectrical energy to light. Light is emitted from active layers ofsemiconductor material sandwiched between oppositely doped layers when avoltage is applied across the doped layers. In order to use an LED chip,the chip is typically enclosed in a package that focuses the light andthat protects the chip from being damaged. The LED package typicallyincludes contact pads on the bottom for electrically connecting the LEDpackage to an external circuit. Conventionally, an LED chip is designedto be packaged either as a discrete light emitter or with a group of LEDchips in an array. The LED chip of the discrete light emitter istypically mounted on a carrier substrate, which in turn is mounted on aprinted circuit board. The LED chips of the array, however, aretypically mounted directed on the printed circuit board without usingthe carrier substrate.

Array products are not conventionally made using the discrete lightemitters as building blocks. The carrier substrate of the discrete lightemitter is typically considered needlessly to occupy space on theprinted circuit board under an array. Moreover, conducting through-holevias through the carrier substrate of the discrete light emitter wouldhave to be reconfigured in order to connect properly to contact pads onthe printed circuit board for each new array design. Thus, no carrierwith a particular set of through-holes vias could be used as a standardbuilding block. The problem of the through-hole vias in the discreteemitters can be solved by electrically connecting the LED chips totraces and contact pads on the top side of the carrier substrate. Buteliminating the through-hole vias by connecting the LED chips to pads onthe top side of the carrier substrate creates the new problem of how toconnect the pads to a power source because the carrier substrate is nolonger electrically coupled to the printed circuit board below.

FIG. 1 (prior art) shows an existing array product 10 with an array oftwenty-six LED chips electrically connected to pads 11 on the top sideof a carrier substrate 12. Array product 10 is the XLamp® MP-L EasyWhiteproduct manufactured by Cree, Inc. of Durham, N.C. In FIG. 1, carriersubstrate 12 is mounted on a metal disk 13 as opposed to on a printedcircuit board. Carrier substrate 12 is attached to metal disk 13 usingthermal glue 14. Array product 10 is inelegantly connected to power byhand soldering individual wires of the positive 15 and negative 16 powercord leads to the pads 11. Array product 10 has no features thatfacilitate connecting the pads 11 on the top side of carrier substrate12 to a power source in the board or plate below. And array product 10is not configured to be incorporated into a group of array products.

A method is sought for using one or more LED chips mounted on a carriersubstrate as a standardized building block to make both a discrete lightemitter as well as an array product of multiple substrates with mountedLEDs.

SUMMARY

Standardized photon building blocks are used to make both discrete lightemitters with one building block as well as array products with multiplebuilding blocks. Each photon building block has one or more LED chipsmounted on a carrier substrate. No electrical conductors pass betweenthe top and bottom surfaces of the substrate. The photon building blocksare held in place by an interconnect structure that is attached to aheat sink. Examples of the interconnect structure include a moldedinterconnect device (MID), a lead frame device or a printed circuitboard.

Landing pads on the top surface of the substrate of each photon buildingblock are attached to contact pads disposed on the underside of a lip ofthe interconnect structure using solder or an adhesive. The lip extendsover the substrate within the lateral boundary of the substrate. In asolder or SAC reflow process, the photon building blocks self-alignwithin the interconnect structure. Molten SAC or solder alloy of thelanding pads wets the metal plated contact pads, and the surface tensionof the molten alloy pulls the landing pads under the contact pads.Conductors on the interconnect structure are electrically coupled to theLED dice in the photon building blocks through the contact pads andlanding pads. The bottom surface of the interconnect structure iscoplanar with the bottom surfaces of the substrates of the photonbuilding blocks.

In an array product, the substrates of multiple photon building blocksare supported by the interconnect structure. The substrates of all ofthe photon building blocks have substantially identical dimensions. Athermal interface material is placed on the upper surface of a heatsink, and the bottom surface of the interconnect structure contacts thethermal interface material. The interconnect structure is fastened tothe heat sink by bolts that pass through holes in the interconnectstructure.

A method of making both a discrete light emitter and an array productusing the same standardized photon building blocks supported by aninterconnect structure. The method includes the step of mounting an LEDdie on a carrier substrate that has no electrical conductors passingfrom its top surface to its bottom surface. A landing pad on the topsurface of the substrate is placed under and adjacent to a contact paddisposed on the underside of a lip of the interconnect structure. Inorder to place the landing pad under the contact pad, the lip of theinterconnect structure is placed over the top surface of the substrateand within the lateral boundary of the substrate.

A conductor on or in interconnect structure is electrically connectingto an LED die on a photon building block by bonding a landing pad to acontact pad. A landing pad can be bonded to a contact pad by heating themetal alloy of the landing pad such that the landing pad aligns with themetal contact pad. Alternatively, the landing pad can be bonded to thecontact pad using anisotropic conductive adhesive film (ACF) technology.For additional details on anisotropic (asymmetric) conductive adhesives,see U.S. patent application Ser. No. 12/941,799 entitled “LED-BasedLight Source Utilizing Asymmetric Conductors” filed on Nov. 8, 2010,which is incorporated herein by reference. After the landing pad isaligned with and bonded to the contact pad, the bottom surface of thesubstrate is substantially coplanar with the bottom surface of theinterconnect structure.

When the method is used to make an array product with multiple photonbuilding blocks, a second lip of the interconnect structure is placedover the top surface of the substrate of a second photon building block,and a second landing pad on the second substrate is placed under andadjacent to a second contact pad under a lip of the interconnectstructure. The second substrate of the second photon building block hasdimensions that are substantially identical to those of the substrate ofthe first photon building block. A second conductor of the interconnectstructure is electrically connected to a second LED die on the secondphoton building block by bonding the second landing pad to the secondcontact pad. After the second landing pad is bonded to the secondcontact pad, the bottom surface of the substrate of the second photonbuilding block is substantially coplanar to the bottom surface of theinterconnect structure.

A thermal interface material is then placed over the upper surface of aheat sink. The bottom surfaces of the interconnect structure and of thesubstrates of the photon building blocks are placed over the thermalinterface material.

A novel light emitting device includes an LED die disposed above asubstrate that includes no electrical conductors between the top andbottom surfaces of the substrate. The device also includes a means forelectrically coupling the LED die to a conductor located outside thelateral boundary of the substrate. The means contacts a landing paddisposed on the top surface of the substrate. The landing pad aligns thesubstrate to a contact pad on the means when the landing pad is heated.The means has a bottom surface that is coplanar with the bottom surfaceof the substrate.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (prior art) is a perspective view of an existing array productwith multiple LED chips electrically connected to pads on the top sideof a carrier substrate.

FIG. 2 is a cross-sectional view of a novel photon building blocksupported by an interconnect structure.

FIG. 3 is a more detailed view of a contact pad connected to a landingpad as shown in FIG. 2.

FIG. 4A is a cross-sectional view of a conductor on an interconnectstructure coupled through a contact pad to a landing pad on a substrate.

FIG. 4B is a perspective view of the path of the conductor of FIG. 4Apassing through a hollow via to the contact pad.

FIG. 4C is a perspective view of the conductor of FIG. 4A passingthrough and entirely covering the inside surface of a hollow via.

FIG. 5 is a cross-sectional view of the conductor of FIG. 4A passingaround the rounded edge of a lip of the interconnect structure.

FIG. 6 shows a landing pad on the substrate bonded to a contact pad onthe underside of a lip of the interconnect structure by an anisotropicconductive adhesive (ACF).

FIG. 7 shows a lead frame interconnect structure with a metal foil layerthat functions both as a conductor of the interconnect structure and asa contact pad that bonds to a landing pad on the substrate.

FIG. 8 shows an interconnect structure made from a printed circuit boardwith a metal layer that functions both as a conductor of theinterconnect structure and as a contact pad that bonds to a landing padon the substrate.

FIG. 9 is a top view of a photon building block that includes four LEDdice surrounded by four landing pads.

FIG. 10 is a top view of another implementation of a photon buildingblock that includes four LED dice surrounded by two landing pads.

FIG. 11A is a top view of two photon building blocks in an interconnectstructure built into an array product.

FIG. 11B is a cross-sectional view through line B-B of the array productshown in FIG. 11A.

FIG. 11C is a cross-sectional view through line C-C of the array productshown in FIG. 11A.

FIG. 12A is a more detailed view of the connection between the landingpad of the substrate and the contact pad of the interconnect structureshown in FIG. 11A.

FIG. 12B shows the contact pad FIG. 12A without the landing pad below.

FIG. 13 is a perspective view of four photon building blocks in aninterconnect structure built into an array product.

FIG. 14 is a flowchart of steps for making both a discrete light emitterand an array product using the same standardized photon building blocks.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 is a cross-sectional view of a photon building block 20 supportedby an interconnect structure 21. Photon building block 20 includes asubstrate 22 upon which an LED die 23 is mounted. Substrate 22 isnon-conductive ceramic. In another implementation, substrate 22 iscrystalline silicon. Landing pads 24 are disposed on the top surface 25of substrate 22. No electrical conductor passes from the top surface 25of substrate 22 to the bottom surface 26 of substrate 22. LED die 23 iselectrically coupled to power solely through the landing pads 24.Thermal interface materials are disposed between LED die 23 andsubstrate 22. A first layer 27 of thermal interface material (TIM) ismade of the same material and deposited in the same process as landingpads 24. In one implementation, pads 24 and first layer 27 are tracesmade of a Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. A second layer 28 ofthermal interface material is deposited on first layer 27. In oneimplementation, second layer 28 is a silver-filled epoxy. LED die 23 isbonded through second layer 28 and first layer 27 to top surface 25 ofsubstrate 22.

LED die 23 is electrically connected through wire bonds 29 to landingpads 24. A thin conformal layer of a wavelength conversion material,such as a phosphor, is formed over LED die 23. Then a clear resinencapsulant, such as silicone, is overmolded over LED die 23 and thewire bonds 29 from about the middle of a landing pad 24 on one side ofupper surface 25 of substrate 22 to about the middle of a landing pad 24on the opposite side of upper surface 25. The silicone forms the shapeof a lens 30. Photon building block 20 includes substrate 22, thelanding pads 24 and everything encapsulated by lens 30.

Interconnect structure 21 supports photon building block 20 through thelanding pads 24. The landing pads 24 are both electrically andmechanically connected to contact pads 31 disposed on the underside of alip of the interconnect structure 21. In one implementation, landingpads 24 are attached to contact pads 31 by a solder paste. An example ofa solder paste is a SAC alloy, such as SAC 305 (96.5% Sn, 3.0% Ag, 0.5%Cu). In another implementation, landing pads 24 are attached to contactpads 31 by an adhesive. An example of an adhesive is an anisotropicconductive adhesive associated with anisotropic conductive film (ACF)technology. In the embodiment of FIG. 2, landing pads are electricallyand mechanically connected to contact pads 31 by solder 48.

In the embodiment of FIG. 2, contact pads 31 are electrically connectedto conductive traces 32 on the top surface 33 of interconnect structure21 by through-hole vias 34. Thus, each conductive trace 32 iselectrically coupled to LED die 23 through via 34, contact pad 31,solder 48, landing pad 24 and wire bond 29. Interconnect structure 21has a bottom surface 35 that is substantially coplanar with bottomsurface 26 of substrate 22.

Photon building block 20 and interconnect structure 21 are attached overa third layer 36 of thermal interface material (TIM) to a heat sink 37.In one implementation, third layer 36 of thermal interface material isthermal glue. In another implementation, third layer 36 is made ofthermal grease, and interconnect structure 21 is attached to heat sink37 by bolts 38. Any small deviations of bottom surfaces 26 and 35 frombeing exactly coplanar are compensated by the thickness of the thermalinterface material, such as the thermal grease. Bolts 38 holdinterconnect structure 21 in place over heat sink 37, and photonbuilding block 20 is held in place by the connection between landingpads 24 and contact pads 31. Thus, substrate 22 is thermally coupledthrough the third layer 36 of TIM to heat sink 37. In oneimplementation, bottom surface 26 of substrate 22 is not directlyconnected to heat sink 37, but is rather “floating” in the layer 36 ofthermal grease. Photon building block 20 is mechanically connected toheat sink 37 only through the bonds between landing pads 24 and contactpads 31. In contrast, carrier substrate 12 of the prior art arrayproduct 10 is attached to the heat sink only by gluing or soldering thebottom surface of substrate 12 to the heat sink.

Compared to a conventional discrete light emitter, a printed circuitboard (PCB) and one layer of TIM have been removed from beneath novelphoton building block 20. In a conventional discrete light emitter, thecarrier substrate sits on a TIM layer over a metal core PCB, which inturn sits on another TIM layer over the heat sink. Using the novelphoton building blocks to make an array product is more economical thanmaking an array product using conventional discrete light emittersbecause the cost of the metal core PCB and an additional TIM layer issaved. Moreover, heat generated by the LED die is more effectivelytransferred from the carrier substrate through one TIM layer directly tothe heat sink than through an additional MCPCB and TIM layer ofconventional discrete light emitters.

In another embodiment, photon building block 20 and interconnectstructure 21 are not attached directly to heat sink 37 over third TIMlayer 36. Instead, a thermal spreader is placed between heat sink 37 andphoton building block 20. Photon building block 20 and interconnectstructure 21 are then attached over third TIM layer 36 to the thermalspreader. An example of a thermal spreader is a vapor chamber.

FIG. 3 shows one of the contact pads 31 of FIG. 2 in more detail and thelanding pad 24 to which the contact pad is connected. Contact pad 31 isa metal trace on interconnect structure 21. In one implementation,interconnect structure 21 is a molded interconnect device (MID). MID 21is a three-dimensional electronic circuit carrier produced by injectinga metalized, high-temperature thermoplastic, such as liquid crystalpolymer (LCP), into a mold. A laser writes the path of the trace on thesurface of MID 21. Where the laser beam oblates the thermoplastic, themetal additive in the thermoplastic forms a very thin conductor path.The metal particles on the conductor path form the nuclei for subsequentmetallization. Metallization baths are used to form successive layers ofcopper, nickel and/or gold traces on the conductor path. For example, alayer of copper forms on the conductor path when the oblatedthermoplastic is placed in a copper bath. Wherever the laser can oblatethe surface of MID 21, three-dimensional circuit traces can quickly beformed.

Contact pad 31 is formed on the underside of a lip 39 of MID 21 afterthe laser oblates the shape of the pad. Metal trace 32 is also formed onthe top surface 33 of interconnect structure 21 in the same manner ascontact pad 31 is formed. Either the laser is articulated so that thelaser beam can be directed at both top surface 33 and the underside of alip 39, or two lasers can be used. In the implementation of FIG. 3,through-hole via 34 is filled with metal before the traces and pads areformed. The metallization baths plate the trace 32 and contact pad 31over the ends of metal via 34.

An electrical and mechanical connection is made between contact pad 31and landing pad 24 by reflowing a solder alloy between the pads. Forexample, a SAC reflow process can be performed where a Sn—Ag—Cu solderalloy is placed at the edge of landing pad 24. When the SAC solder ismelted, the solder wets the metal of contact pad 31. Then the surfacetension of the molten SAC alloy pulls landing pad 24 under contact pad31. A bond is then formed between landing pad 24 and contact pad 31 whenthe SAC alloy cools and solidifies.

FIG. 4A shows another implementation of how a metal trace 40 on MID 21is electrically coupled to landing pad 24 on substrate 22. Instead ofvia 34 filled with metal, as in FIG. 3, MID 21 of FIG. 4A includes ahollow tapered via 41. Hollow via 41 is formed using a conical plug inthe molding process that forms the molded interconnect device 21. Thelaser oblates a conductor path across top surface 33, around the insidesurface of via 40, and then on the underside of a lip 39 to form theshape of contact pad 31. The conductor path and pad shape are thenplated in a metallization bath. FIG. 4B shows the conductor path of thelaser in more detail. The conductor path can be much wider than thewidth of the laser. The laser can make many passes to create a wideconductor path, such as the one shown in FIG. 4C. In FIG. 4C, the entirepartially conical-shaped inside surface of hollow via 41 is oblated andwill be plated in a metallization step.

FIG. 5 shows another implementation of how a metal trace 42 on MID 21 iselectrically coupled to landing pad 24 on substrate 22. Lip 39 of MID 21is given a rounded edge. The laser makes a continuous conductor pathacross top surface 33, around the rounded edge and then on the undersideof a lip 39.

FIG. 6 shows an alternative way of electrically and mechanicallycoupling contact pad 31 to landing pad 24 that does not involve solder.An anisotropic conductive adhesive is used to connect contact pad 31 tolanding pad 24 in FIG. 6 instead of the bond formed using solder reflowas shown in FIG. 3. Because solder is not used, photon building block 20does not self-align within interconnect structure 21, but must beaccurately positioned before the adhesive cured. Anisotropic conductiveadhesive film (ACF) technology involves conductive balls dispersed in anadhesive. For example, Au-coated polymer balls or Ni-filled balls aredispersed in an epoxy adhesive. The surfaces being electrically coupledare then pressed together to the diameter of the balls. The adhesive isthen cured, for example by heating. An electrical contact is made inthose areas where the balls touch both surfaces. The anisotropicconductive adhesive is not conductive in those areas where the balls arestill dispersed in the cured adhesive. In FIG. 6, the anisotropicconductive adhesive mechanically connects pad 31, the underside of lip39 and the entire side of MID 21 to landing pad 24 and the side ofsubstrate 22. However, an electrical connection is made only betweenthose areas of contact pad 31 and landing pad 24 that were pressedtogether to within the diameter of the conductive balls.

FIG. 7 shows another implementation of how a conductor 44 oninterconnect structure 21 is electrically coupled to landing pad 24 onsubstrate 22 using solder. Interconnect structure 21 of FIG. 7 is a leadframe instead of a molded interconnect device. A metal foil 44 isstamped in the form of the conductors, leads and “gull wings” requiredfor the package of the discrete light emitter or array product. Leadframe structure 21 is then made by injection molding a liquid crystalpolymer (LCP) 45 around a stamped metal foil 44. The metal foilfunctions both as the conductor 44 as well as the contact pad 31. Theend of the metal foil under lip 39 can be stamped in the shape of acontact pad with a shape corresponding to the shape of landing pad 24 inorder to facilitate self-alignment during a solder reflow process.

FIG. 8 shows another implementation of a conductor 46 in interconnectstructure 21 that is electrically coupled to landing pad 24 on substrate22 using solder. Interconnect structure 21 of FIG. 6 is a printedcircuit board (PCB). For example, interconnect structure 21 is an FR-4printed circuit board made of woven fiberglass fabric 46 with an epoxyresin binder. FR-4 PCB 21 has several metal layers. One of the metallayers 47 functions both as the conductor and as the contact pad 31. Theend of metal layer 47 under lip 39 can be formed in a shapecorresponding to the shape of landing pad 24 in order to facilitateself-alignment during a solder reflow process.

FIG. 9 is a top view of a photon building block 50 that includes fourLED dice 51-54. The same material is used to make the four landing pads55-58 as well as the first TIM layer 27 beneath the four LEDs. Secondlayer 28 of thermal interface material is deposited on first layer 27beneath each LED die and is not visible in the view of FIG. 9. LED die51 and 54 are electrically connected in series between landing pads 55and 58. Two wire bonds connect each LED die to a landing pad and toanother LED die. For example, wire bonds 59-60 connect LED die 51 tolanding pad 55. The dashed circle indicates the extent to which siliconelens 30 encapsulates the components on substrate 22. Lens 30 extends toabout the middle of the landing pads 55-58. The diameter of lens 30 isabout twice as long as each side of the 2×2 array of LED dice so as toallow most of the emitted light to reach the surface of lens 30 withinthe critical angle required for the light to escape from the lens.

Photon building block 50 can be used to make both a discrete lightemitter with a single photon building block as well as an array productwith multiple photon building blocks. Interconnect structure 21 caneasily be molded or configured to incorporate photon building block 50into a plurality of different discrete light emitter products. The boltholes through which bolts 38 attach interconnect structure 21 to heatsink 37 can easily be repositioned without changing the design of photonbuilding block 50. And the conductors that are electrically coupled tothe LED dice can easily be retraced using a laser to write theconductive paths over the surface of the molded interconnect device.Thus, a new emitter need not be tested and qualified each time a newlight emitter product is made using photon building block 50.

FIG. 10 is a top view of a photon building block 61 with only twolanding pads 62-63 that surround the four LED dice 51-54. As with photonbuilding block 50 of FIG. 9, the landing pads 62-63 and the first TIMlayer 27 beneath the four LEDs are made from the same material, such asa Cu—Ni—Au alloy or a Cu—Ni—Ag alloy. The landing pads 62-63 have pointsthat extend to the four corners of substrate 22. In a SAC reflow step,the solder alloy that extends farther toward the corners of substrate 22than with landing pads 55-58 can more precisely align substrate 22beneath the contact pads of the interconnect structure 21. The smallersurface area of landing pads 62-63 beneath the contact pads, however,results in a weaker mechanical connection between the landing pads andcontact pads.

FIG. 11A is a top view of photon building block 50 of FIG. 9 built intoan array product with another photon building block 64. A moldedinterconnect device 65 holds the photon building blocks 50 and 64 inplace in a 1×2 array. The area of MID 65 is denoted by cross hatching.MID 65 has six lips that extend over the corners of photon buildingblocks 50 and 64 and hold those corners in place. For example, a lip 39of MID 65 extends over the upper right corner of substrate 22, and acontact pad on the underside of lip 39 is electrically and mechanicallyconnected to a portion of landing pad 55 using solder or an adhesive.MID 65 also has another lip 66 that extends over both the upper leftcorner of photon building block 50 and the upper right corner of photonbuilding block 64. Separate contacts pads under lip 66 are bonded tolanding pad 56 of photon building block 50 and to a landing pad 67 ofphoton building block 64. MID 65 has four holes 68 for the bolts 38 thatattach the array product to heat sink 37.

FIG. 11B is a cross-sectional view through line B-B of the 1×2 arrayproduct shown in FIG. 11A. FIG. 11B shows how contact pad 31 on theunderside of lip 39 is electrically and mechanically connected to aportion of landing pad 55. FIG. 11B also shows portions of the contactpads under lip 66 that bond to landing pads 56 and 67. FIG. 11C is across-sectional view through line C-C of the 1×2 array product shown inFIG. 11A. The contact pads of MID 65 are not visible in the crosssection of FIG. 11C.

FIGS. 12A-B illustrate the connection between landing pad 55 and contactpad 31 of FIG. 11A in more detail. Contact pad 31 has the same outlineshape as a corner of the landing pad 55 below. A solder reflow processcan be performed with the contact pads on top aligning to solder on thelanding pads below, or the process can be inverted. The structure ofFIG. 11B can be inverted such that the landing pads are on top of thecontact pad and align to molten solder on the contact pads.

In a SAC reflow process when the SAC solder on landing pad 55 is melted,the solder wets the metal of contact pad 31. Then the surface tension ofthe molten SAC solder pulls contact pad 31 over the portion of landingpad 55 that has the same shape. The four landing pads at the corners ofsubstrate 22 are thereby each pulled towards the contact pads of thesame shape and align photon building block 55 within the frame of MID65. When the SAC solder cools and solidifies, bonds are formed betweenthe landing pads and the contact pads. The solder bonds between thelanding pads and the contact pads hold the photon building blocks inplace such that the bottom surfaces of the substrates are substantiallycoplanar with bottom surface 35 of MID 65 even when the array product isnot attached to a heat sink. The array product can be shipped unattachedto any submount, such as a heat sink. The bonds between the landing padsand the contact pads are sufficiently strong to maintain the mechanicalintegrity of the array product despite the vibrations and bumpingusually encountered in shipping.

FIG. 12A also shows a conductor 69 on the top surface of MID 65 that iselectrically coupled to first LED die 51. Conductor 69 is a metal traceformed by plating a path oblated by a laser. Metal trace 69 iselectrically coupled to LED die 51 through a solid metal via 70, contactpad 31, solder 48 or an ACF adhesive, landing pad 55 and wire bonds59-60. The dashed line designates the extent of silicone lens 30.

FIG. 12B shows contact pad 31 of FIG. 12A without the landing pad 55 ofphoton building block 50 below. The triangular cross-hatched area aroundcontact pad 31 is lip 39 that extends over the upper right corner ofsubstrate 22 of photon building block 50. FIG. 12B also shows a lip 71of MID 65 that extends over the lower right corner of substrate 22. Thearea of MID 65 shown with a latticed pattern is filled with liquidcrystal polymer from top surface 33 to bottom surface 35 of theinterconnect structure.

FIG. 13 is a perspective view of photon building block 50 of FIG. 9built into an array product with three other photon building blocks. Amolded interconnect device 72 holds the photon building blocks in placein a 2×2 array. The interconnect structure 72 includes bridges betweenthe photon building blocks that support a center island 73 beneath whichthe contact pads attach to the inner landing pads of the four photonbuilding blocks. As MID 72 is formed in a molding process, non-planarsurfaces are easily made. MID 72 has curved walls 74 around the photonbuilding blocks that are coated with a reflective material, such as ametal film. The curved walls can be shaped to impart a parabolicreflection to the light emitted from the photon building blocks. Theconductors that connect to the contact pads (not shown in FIG. 13) aredrawn with a laser over the curved walls and then plated in ametallization bath. The conductors are connected to the contact padswith through hole vias or hollow vias as shown in FIGS. 3-4. AlthoughFIG. 13 depicts a 2×2 array of photon building blocks supported by aninterconnect structure, arrays with other dimensions can also be made ina similar manner using bridges between the photon building blocks.

FIG. 14 is a flowchart illustrating steps 75-81 of a method of makingboth a discrete light emitter and an array product using the samestandardized photon building blocks that have one or more LED chipsmounted on a carrier substrate. The method can be used to connect photonbuilding blocks in any configuration, such as in parallel or in series,to achieve the desired light output and power consumption of theresulting array product. The method easily connects the photon buildingblocks electrically, mechanically and thermally to other structures ofthe ultimate lighting product. The electrical connections to the powersource can easily be configured. The orientation of the photon buildingblocks can easily be aligned with reflectors and lenses of the lightingproduct. The position of the bolts that mechanically connect theinterconnect structure to the lighting product can easily bereconfigured without changing the photon building blocks. And theinterconnect structure can easily be configured to thermally connectwith a multitude of heat sinks.

In a first step 75, light emitting diode die 51 is mounted on carriersubstrate 22 of first photon building block 50. Substrate 22 has noelectrical conductors passing from its top surface 25 to its bottomsurface 26. LED die 51 is attached to substrate 22 using first TIM layer27 and second TIM layer 28. Landing pad 55 on top surface 25 ofsubstrate 22 is made from the same material and in the same process asfirst TIM layer 27.

In step 76, landing pad 55 is placed under and adjacent to contact pad31, which is disposed on the underside of lip 39 of interconnectstructure 65. In so doing, lip 39 is placed over top surface 25 ofsubstrate 22 and within the lateral boundary of substrate 22. At theconclusion of step 76, the photon building blocks are placed withininterconnect structure 65.

In step 77, conductor 32 of interconnect structure 65 is electricallyconnecting to LED die 51 by bonding landing pad 55 to contact pad 31.The pads are bonded by either solder or an ACF adhesive. When usingsolder, landing pad 55 is bonded to contact pad 31 by heating a metalalloy on landing pad 55 such that the landing pad aligns with the metalcontact pad. When using anisotropic conductive adhesive film (ACF)technology to bond the pads, the photon building blocks are accuratelypositioned within interconnect structure 65, and landing pad 55 isbonded to contact pad 31 when the ACF adhesive is cured by heating.After landing pad 55 is aligned with and bonded to contact pad 31,bottom surface 26 of substrate 22 is substantially coplanar with bottomsurface 35 of interconnect structure 65.

In step 78, when the method of FIG. 14 is used to make an array product,second lip 66 of interconnect structure 65 is placed over the topsurface of a second substrate, and a second landing pad 67 is placedunder and adjacent to a second contact pad attached to the underside oflip 66. The second substrate is part of second photon building block 64and has dimensions that are substantially identical to those of thefirst substrate 22. A second LED die disposed on the second substratehas dimensions that are substantially identical to those of LED die 51on first substrate 22.

In step 79, when the method of FIG. 14 is used to make an array product,a second conductor of interconnect structure 65 is electricallyconnected to the second LED die that is disposed on the second substrateby bonding second landing pad 67 to the second contact pad attached tothe underside of lip 66. For example, landing pad 67 can be bonded tothe second contact pad using a SAC reflow process or by using ananisotropic conductive adhesive. After second lip 66 is placed over thetop surface of the second substrate and landing pad 67 is bonded to thecontact pad on the underside of lip 66, the bottom surface of the secondsubstrate is substantially coplanar to bottom surface 35 of interconnectstructure 65.

In step 80, thermal interface material 36 is placed over the uppersurface of heat sink 37. The upper surface of heat sink 37 need not beplanar except under substrate 22 and the area directly around thesubstrate. For example, the upper surface of heat sink 37 can be themostly curved surface of a luminaire. Likewise, bottom surface 26 ofsubstrate 22 and bottom surface 35 of interconnect structure 65 need notbe coplanar except in the immediate vicinity of substrate 22.

In step 81, substrate 22 and interconnect structure 65 are placed overthermal interface material 36 such that thermal interface material 36contacts both bottom surface 26 of substrate 22 and bottom surface 35 ofinterconnect structure 65. When the method of FIG. 14 is used to make anarray product, the second substrate of photon building block 64 is alsoplaced over thermal interface material 36 such that thermal interfacematerial 36 contacts the bottom surface of the second substrate. Themethod of FIG. 14 can also be used to make an array product with morethan two photon building blocks, such as the array product shown in FIG.13.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A device comprising: a substrate comprising asurface; a continuous thermal interface material; a light emitting diode(LED) die; and a landing pad disposed on the surface of the substrate,wherein the LED die is electrically coupled to the landing pad; whereinthe landing pad is configured to provide an electrical connection to acontact pad disposed on an interconnect structure, with the contact padbeing disposed above the substrate; wherein the continuous thermalinterface material is in contact with both the substrate and theinterconnect structure; and wherein the landing pad is configured toprovide a mechanical connection between the landing pad and the contactpad sufficient to hold the interconnect structure to the substrate. 2.The device of claim 1, wherein the substrate is free of holes or mousebites to mechanically attach the substrate to a heat sink.
 3. The deviceof claim 1, wherein the substrate is a closed substrate.
 4. The deviceof claim 1, wherein the LED is within 3 mm of a lateral boundary of thesubstrate.
 5. The device of claim 1, wherein the substrate comprises alateral boundary having the shape of a polygon, the polygon comprising amaximum of four sides.
 6. The device of claim 1, wherein the landing padis positioned on a lateral boundary of the substrate.
 7. The device ofclaim 6, further comprising a plurality of LED dies and a plurality oflanding pads, wherein the plurality of LED dies are electricallyconnected in series between the plurality of landing pads.
 8. The deviceof claim 1, further comprising: an array of LED dies; and a lens,wherein in the lens is twice as long as each side of the array of LEDdies so as to allow most of the emitted light to reach the surface ofthe lens.
 9. The device of claim 1, further comprising a lens partiallycovering the landing pad.
 10. The device of claim 1, further comprisingan anisotropic conductive adhesive used to connect the contact pad tothe landing pad.
 11. The device of claim 1, wherein the thermalinterface material is a thermal grease, and wherein the substrate isheld in place by the connection mechanical connection between thelanding pad and the contact pad.
 12. The device of claim 1, wherein thecontinuous thermal interface material is disposed on a surface of thesubstrate opposite the landing pad.
 13. The device of claim 1, whereinthe continuous thermal interface material is in direct contact with boththe substrate and the interconnect structure.
 14. A device comprising: asubstrate comprising a pair of opposing first and second surfaces; acontinuous thermal interface material disposed directly on the firstsurface of the substrate; a light emitting diode (LED) die; and alanding pad disposed on the second surface of the substrate, wherein theLED die is electrically coupled to the landing pad; wherein the landingpad is configured to provide an electrical connection to a contact paddisposed on an interconnect structure, with the contact pad beingdisposed above the substrate; wherein the continuous thermal interfacematerial is in direct contact with both the substrate and theinterconnect structure; and wherein the landing pad is configured toprovide a mechanical connection between the landing pad and the contactpad sufficient to hold the interconnect structure to the substrate.